1. Field of the Invention
The present invention relates in general to telecommunication systems, and more particularly, to an arrangement and method of proprietary control protocol and messages that are used in the functional operation of a digital telephone system.
2. Description of the Prior Art
Prior to the present invention, remote telephone consoles were implemented as described in U.S. Pat. No. 4,751,696, "CENTREX ATTENDANT CONSOLE INTERFACE". But this implementation was limited because:
1. It required a total of six wires between the Central Office (CO) and the console; PA1 2. The analog signal is not digitized until reaching the CO, thereby allowing noise to be induced; PA1 3. The line card (CONI) does not provide any call processing functions; PA1 4. The data channel is limited to a low BAUD rate; and PA1 5. All customer information is stored in the central office's central computer or the remote console.
Most organizations desire each secretary to have a telephone instrument console for answering unattended phones, determining who is using the phone, intercepting calls, etc. These features are generally present if the organization purchases a Private Branch Exchange (PBX); however, as stated in U.S. Pat. No. 4,751,696, the telephone industry developed CENTREX to provide many of the same features without the initial capital or maintenance requirements. But, because of the limitation stated above, the number of consoles per CO was limited.
Because of the limited number of consoles, the telecommunications industry developed its CENTREX features to function on a standard telephone instrument. This was accomplished by using "access" codes to indicate which feature was to be used. Each feature generally required a distinct access code.
To simplify the features, and reduce the number of access codes that must be memorized, a programmable telephone instrument was developed. The programmable telephone instrument had feature buttons that sent the appropriate access code to the CENTREX system. But to answer an unattended telephone instrument a secretary must either forward the call from the unattended telephone to their console or be able to hear the unattended telephone ring and press the correct access code (or feature button). To solve this problem, each line to be monitored was split and sent to both the telephone and the secretarial console. When a telephone rings (or is busy) the secretarial console indicates which line is ringing. But, the number of wires connected to the console can quickly become prohibitive.
Presently known implementations of programmable telephones load the operational and functional software into the instrument itself. The "Intelligent" digital telephone communicated or passed control and operational messages directly to the host system central processor complex. Since modern CO exchanges operate in real time, software processing of such real time requests for operational service from a plurality of "Intelligent" telephone instruments severely impacts the operation of the CO exchange.
Further, the control protocol software used by the "smart" telephone instrument for its operation is usually resident in Read Only Memory (ROM) within a processor complex of the telephone instrument. Any operational changes required to be made to the instrument entailed replacement of the ROM.
It is more advantageous to provide a digital telephone instrument that is basically "less intelligent" that interfaces and communicates to a digital telephone controller resident in the line interface of the CO. In this particular configuration the digital telephone sends requests to the controller, and the controller sends back responses to the digital telephone for controlling its functions. Only those messages required for call processing are transmitted from the controller to the CO central processing complex. All software required in the functional operation of the features of the digital telephone instrument are resident in the controller at the CO site, where the functional operation for each telephone can be changed easily by maintenance technicians without hardware updates.
It therefore becomes the object of the present invention to provide an arrangement and method of proprietary control protocol and messages that are used to control the functional operation of a digital telephone instrument and its call processing system.